Configurable chassis guidance system and method

ABSTRACT

A configurable chassis guidance system and method are described. The system may be practiced as a chassis and/or a module or an element thereof (e.g., a mating guide). The system and method allow reconfiguration of multiple modules of various module widths without the need for removal or reinstallation of module guides mounted on the chassis. As an example, a single-width module may be removed and replaced by a double-width module or quadruple-width module without removing module guides used to engage the single-width module. As another example, a double-width module or quadruple-width module may be removed and replaced by a single-width module without removing module guides used to engage the double-width module or quadruple-width module. The system and method may be practiced so as not to impair compatibility of modules with card edge module guides that engage an edge of a circuit board of a module.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of application number11/253,081, filed Oct. 17, 2005. The present application claims priorityunder 35 U.S.C. § 119(e) to the following United States provisionalapplications: Appli. Ser. No. 60/779,906, filed Mar. 6, 2006.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to electronic systems and moreparticularly to modular electronics systems having a chassisconfigurable for a variety of modules.

(2) Description of the Related Art

While some electronic systems are a manufactured in a fixed format thatdoes not include or accept modules to allow flexibility in configuringthe hardware elements of the system, many electronic systems are modularin nature and include chassis structures and connectors to acceptmodules. However, typical modular electronic systems impose constraintson modules, for example, requiring that all modules be of the same size,etc. It would be useful for a system to be able to accept modules ofvarying sizes, for example to accommodate modules supporting differentnumbers of communication channels.

In the prior art, U.S. Pat. No. 6,646,890, issued to Byers et al.(hereinafter Byers) describes mounting of mezzanine circuit boards to abase board. Byers describes guide rails that can be moved to provide anew spacing to accommodate a different width mezzanine board withouthaving to take the supporting base board out of service. However, theguide rails of Byers suffer several disadvantages. While Byer describesguide rails to accommodate a plurality of nested mezzanine boards, itappears that the widths of the nested mezzanine boards are constrainedby the guide rails such that nested mezzanine boards cannot be ofdifferent widths. Moreover, as the guide rails appear to be separatefrom the mezzanine circuit boards, the guide rails of Byers appear tohave the potential for causing logistical complexities and delays if,for example, a guide rail is not available at the time a mezzaninecircuit board is desired to be installed.

The utility, practicality, and convenience of a modular system would beenhanced if it were able to be configured (e.g., installed in an initialconfiguration or reconfigured) without the need for special parts and/ordisturbance to modules not involved in the configuration. For example,two one-port modules were to be replaced by one two-port module, itwould be desirable to avoid a need to install or remove special parts.Thus, a technique for configurably accommodating modules of varioustypes (e.g., sizes) is needed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention may be better understood, and its features madeapparent to those skilled in the art by referencing the accompanyingdrawings.

FIG. 1 is a flow diagram illustrating a method in accordance with atleast one embodiment of the present invention.

FIG. 2 is a flow diagram illustrating a method in accordance with atleast one embodiment of the present invention for when a circuit boardhas been populated to provide a first set of customer connectors and isto be populated to provide a first set of intermediate connectors.

FIG. 3 is a flow diagram illustrating a method in accordance with atleast one embodiment of the present invention for when a circuit boardhas been populated to provide the first set of intermediate connectorsand is to be populated to provide the first set of customer connectors.

FIG. 4 is a block diagram illustrating several configurations that maybe provided in accordance with at least one embodiment of the presentinvention.

FIG. 5 is a block diagram illustrating several relationships ofcomponents in accordance with at least one embodiment of the presentinvention.

FIG. 6 is a plan view diagram illustrating an example of a system inaccordance with at least one embodiment of the present invention.

FIG. 7 is a prospective view diagram illustrating an example of a systemin accordance with at least one embodiment of the present invention.

FIG. 8 is an elevation view diagram illustrating an example of a systemin accordance with at least one embodiment of the present invention.

FIG. 9 is a cross-sectional diagram illustrating an example of a moduleguide subsystem in accordance with at least one embodiment of thepresent invention.

FIG. 10 is an elevation view diagram illustrating an example of a moduleguide subsystem in accordance with at least one embodiment of thepresent invention.

FIG. 11 is a plan view diagram illustrating an example of a module guidesubsystem in accordance with at least one embodiment of the presentinvention.

FIG. 12 is a prospective view diagram illustrating an example of asystem incorporating a stackable module guide subsystem in accordancewith at least one embodiment of the present invention.

FIG. 13 is an elevation view diagram illustrating an example of a systemincorporating a stackable module guide subsystem in accordance with atleast one embodiment of the present invention.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION OF THE INVENTION

A configurable chassis guidance system and method are described. Thesystem may be practiced as a chassis and/or a module or an elementthereof (e.g., a mating guide). The system and method allowreconfiguration of multiple modules of various module widths without theneed for removal or reinstallation of module guides mounted on thechassis. As an example, a single-width module may be removed andreplaced by a double-width module or quadruple-width module withoutremoving module guides used to engage the single-width module. Asanother example, a double-width module or quadruple-width module may beremoved and replaced by a single-width module without removing moduleguides used to engage the double-width module or quadruple-width module.The system and method may be practiced so as not to impair compatibilityof modules with card edge module guides that engage an edge of a circuitboard of a module.

In accordance with at least one embodiment, a guidance system forpluggable circuit boards that may be plugged into an electronics chassisis described. The system permits the installation of variable widthboards in a common chassis slot without any modification to the chassisbeing required. One or more embodiments may be applied to electronicsystems in the field of telecommunications and/or systems in otherfields such as computing platforms, electronic test equipment, etc.

It is useful to be able to plug different types of modules (e.g.,circuit cards comprising circuit boards) (for example, those providingdifferent flavours of customer interfaces—such as T1, 10/100, optical,OC3, etc.) into a common slot in an electronics chassis (e.g., anelectronics chassis housing horizontally oriented boards). The modulesmay be of variable widths. Accordingly, the guidance mechanism forinsertion and/or removal of the modules should accommodate the variablewidths while imposing few restrictions on the usable circuit board areaof the cards. In addition, it is not desirable to require the end userto perform any field modifications to the chassis in order to insert anyof the various width card options (e.g., no removal or addition ofguidance parts should be necessary in order to permit installation ofvarious widths of cards in the same slot). For example, if a card edgemodule guide were required to be removed for installation of a widermodule and were required to be reinstalled for replacement of the widermodule with a narrower module, the card edge module guide might bemisplaced between the time of removal and reinstallation. If the cardedge module guide were unavailable when it was to be reinstalled, areplacement would have to be procured, which could greatly complicateand delay the process, or, if a replacement were no longer available,the entire chassis might have to be replaced. Thus, in accordance withat least one embodiment, the need for reconfiguration of card edgemodule guides may be avoided.

However, at least one embodiment provides compatibility with othersystems, such as those that involve removal and reinstallation of cardedge module guides. For example, PICMG AMC.0 Advanced Mezzanine CardShort Form Specification, Version D0.9a (Draft), Jun. 15, 2004, coversvarious alternatives for mounting mezzanine cards onto a carrier (orbase) printed circuit board (PCB). The specification covers guide railsand connector formats as well as special carrier adaptations such ascut-outs to accept stacked mezzanine cards. While components describedin the specification suffer from the shortcomings described above, itmay be desirable to implement at least one embodiment of the presentinvention so as not to be incompatible with such components.Accordingly, at least one embodiment may be practiced to provide achassis that may be used to engage modules offering the benefitsdescribed herein and/or other mezzanine cards, such as PICMG AMC.0mezzanine cards. As another example, at least one embodiment may bepracticed to provide modules that may be used to engage a chassisoffering the benefits described herein and/or other chassis, such as aPICMG AMC.0 chassis.

In accordance with at least one embodiment, an offset guide rail isprovided on one side (e.g., the bottom side) of the card as the primaryguidance mechanism for the card. This differs from traditional methodswhich use the card edge sliding in a card edge guide as the primaryguidance mechanism. The offset guide rail elevates the card above theguidance mechanism in the chassis thus permitting great variability inthe width of the cards which can plug into a given slot, as the cardssimply slide above the chassis guiding mechanism during insertion. Forcards that span an unused module guide, components on the side of thecard facing the unused module guide (e.g., the bottom side) should, inthe immediate area of the unused module guide, extend no farther inheight away from the card surface than the height of the gap definedbetween the card surface and the unused module guide so as to preventcontact between the components and the unused module guide. When achassis as described herein is used in conjunction with modules asdescribed herein, no chassis modification is required in order to removea module of a first width and install a module of another width in itsplace—i.e., the chassis slot is universal. In addition, in accordancewith at least one embodiment, the offset guide rail (e.g., mating guide)and/or the module guide includes large cutouts to allow cooling air toflow on the bottom side of the card. Furthermore, if the surface of acircuit card upon which the offset guide rails are mounted are left freeof components in the vicinity of side edges, then the circuit card canbe implemented to be compatible with both the PICMG AMC specificationand a guidance mechanism featuring the benefits of the presentinvention. Still further, a similar guidance mechanism to that mountedon the chassis (e.g., T-bars or halves of T-bars, which may, forexample, be described as L bars or C bars) can be mounted on the topside of a card to accept the offset guide rails of another card, therebyenabling vertical stacking of cards in the system chassis.

At least one embodiment may be practiced so as to give a customercomplete flexibility for the configuration of card types in a givenchassis slot. A customer can populate/repopulate a chassis with avariety of combinations of card widths in a given slot without having toperform any modifications to the chassis to add or remove a guidancefeature. For example, possible combinations in a given chassis slothaving a total width sufficient to accommodate four single-width cardsare as follow: 4× single width cards, 2× single width+1× double width,2× double width, 1× single width+1× triple width, and 1× quadruplewidth. Not only are all of those combinations possible, but all possiblepermutations may be practiced. For example, two single-width cards maybe situated to the left of one double-width card or to the right of onedouble-width card, or one single-width card may be situated to the leftof one double-width card and another single-width card may be situationto the right of the double-width card.

In accordance with at least one embodiment, apparatus may comprise asystem having a chassis comprising at least one module guide and atleast one module comprising at least one mating guide to engage the atleast one module guide. In accordance with at least one embodiment,apparatus may comprise a chassis comprising at least one module guide toengage at least one mating guide of at least one module. In accordancewith at least one embodiment, apparatus may comprise at least one modulecomprising at least one mating guide to engage at least one module guideof a chassis. Embodiments may allow use of multiple-unit-wide modules(e.g., 2×, 3×, 4× wide modules) providing clearance to preventcomponents mounted on the modules from contacting at least one unusedmodule guide on the chassis. Embodiments may utilize at least oneadditional module guide on a first module to engage at least oneadditional mating guide of a second module to permit stacking (e.g.vertical stacking) of cards in a chassis. Accordingly, several modulesmay be disposed next to each other (e.g., having their circuit boards inthe same plane), while one or more other modules may be stacked withrespect to those one or more of those several modules. Thus, atwo-dimensional array of modules may be made accessible to a customerand the customer given an ability to replace any one or more of thosemodules without disturbing other modules. By providing unpopulated areas(i.e., areas unobstructed by electronic components or other objects)along edges of a circuit board of a module, the module can be made to becompatible with card edge module guides while also being compatible withmodule guides described herein that provide advantages over card edgemodule guides.

A method and apparatus for an electrical system architecture capable ofproviding fixed or modular components, for example, interfaceconnectors, is provided. Fixed components allow product cost to beminimized. Modular components provide flexible configurability ofproducts. In accordance with at least one embodiment of the presentinvention, an electrical system architecture capable of providing fixedor modular components minimizes costs such as design, production, andcustomer support costs while being able to provide a range of productvariants.

As one example, at least one embodiment of the present invention may beused to provide a circuit board, such as a printed circuit board (PCB),that is designed for several interface ports, for example, 24 fixed10-megabit-per-second/100-megabit-per-second (10 Mbps/100 Mbps or10/100) ethernet interface ports, two fixed gigabit ethernet (GE)interface ports, or, alternatively, several (e.g., four) pluggablemodules.

In accordance with at least one embodiment of the present invention, asingle PCB, for example, one having dimensions of 15.45″×11.00″, can beused to implement either a fixed or fully modular interface system. Oneexample of a fixed interface system comprises three fixed 2×6 RJ45connectors and two fixed GE small-form-pluggable (SFP) interface portsstuffed on the PCB. Additional metal work wraps around such a fixed PCBassembly to provide a low cost, physically small, and attractiveproduct.

In the past, providing a modular version from such a product designwould typically consist of a complete re-design of the PCB. However, inaccordance with at least one embodiment of the present invention, byde-stuffing (or not stuffing) the port interface connectors (e.g., RJ45and SFP connectors), adding modules guides, and wrapping the PCB in adifferent metal wrap, a fully modular product variant can be providedwith a very short time to market.

In accordance with at least one embodiment of the present invention,features may be provided to facilitate use of a common circuit board forfixed and modular configurations and conversion between fixed andmodular configurations. As one example, a removable card guide mechanismfor the modules may be provided. As another example, a mountingtechnique may be used to maintain the vertical position of the commoncircuit board in such a way as to allow airflow over the modules andcircuit board for both fixed and modular configurations. As anotherexample, the common circuit board may be mounted upside down to keepmounting screws from interfering with module insertion.

In accordance with at least one embodiment of the present invention, acommon circuit board design may be used for various I/O portconfigurations, including fixed and replaceable I/O ports, therebyreducing design costs. By allowing use of a common circuit board formultiple configurations, a faster time to market can be obtained forimplementations having new I/O port configurations, e.g., ifreplaceable/modular I/O ports are required in a new product based on aproduct that featured a fixed interface.

FIG. 1 is a flow diagram illustrating a method in accordance with atleast one embodiment of the present invention. In step 101, anunpopulated circuit board is produced. Circuit boards typically comprisea insulating substrate, for example, a flame retardant type 4 (FR4)glass-fiber/epoxy-resin composite substrate with one or more layers ofconductive material, such as metal, for example, copper. Conductivelayers may be provided on external surfaces of the substrate and/orinternal to the substrate. Conductive material may be selectivelyremoved from portions of the conductive layer or layers to formconductive patterns, which may be referred to as printed circuits. Thus,such circuit boards may be referred to as printed circuit boards (PCBs).Printed circuits provide conductive interconnects for components thatmay be mounted on PCBs, for example, passive components, such asresistors, capacitors, and/or inductors; active components, such asintegrated circuits and/or transistors; and/or other components, such asconnectors, switches, input devices, and/or output devices. Afterestablishing printed circuits on a PCB, additional steps may beundertaken, for example, drilling holes in the PCB, applying (e.g.,plating) conductive material to line at least one of the holes so as toconductively bridge portions of different conductive layers of the PCB,applying at least one solder mask layer over at least a portion of atleast one surface of the PCB to protect conductive material and inhibitsolder contact with protected areas, and/or applying (e.g,silk-screening) printed nomenclature to identify component locations.Any or all such steps may be performed to produce an unpopulated PCB,which is a PCB that has not yet been populated by components (i.e., towhich components have not yet been added).

In step 102, the circuit board is populated with components. Step 102may comprise steps 103, 104, 105, 106, 107, and/or 108. In step 103, thecircuit board is populated with components common to circuit boardsintended to be populated with customer connectors and circuit boardsintended to be populated with intermediate connectors. In step 104, adecision is made as to whether the circuit board is to be populated withcustomer connectors (i.e., connectors accessible from an exterior of anenclosure of the circuit board and adapted to be used for connectionsexternal to the enclosure) or intermediate connectors (i.e., connectorsaccessible from an interior of the enclosure and adapted to be used forconnections to interface modules to be substantially contained withinthe enclosure, wherein the interface modules preferably provide customerconnectors).

When a decision is made in step 104 to populate the circuit board withcustomer connectors, the process continues at step 105. In step 105, thecircuit board is populated with customer connectors. In step 106, thecircuit board is populated with interface electronics to support thecustomer connectors. Such interface electronics are preferably installedon a second surface (e.g., underside) of the circuit board opposite afirst surface of the circuit board, wherein the first surface is thesurface on which intermediate connectors would have been installed hadthe decision been made to populate the circuit board with intermediateconnectors. The first surface is preferably a first planar surface, andthe second surface is preferably a second planar surface.

From step 106, the process continues to step 109. In step 109, thecircuit board is installed in a customer-connector-compatible enclosure.The customer-connector-compatible enclosure defines at least oneaperture to allow access to at least one customer connector from theexterior of the customer-connector-compatible enclosure. Following step109, the initial zero-option (i.e., options such as modules have not yetbeen installed) configuration has been completed. From 109, the processcontinues to step 110. In step 110, the product is used, for example, byconnecting equipment external to the customer-connector-compatibleenclosure to at least one customer connector.

When a decision is made in step 104 to populate the circuit board withintermediate connectors, the process continues to step 107. In step 107,the circuit board is populated with intermediate connectors. In step108, the module guides are installed. The module guides aid in alignmentof modules as they are inserted and/or removed from theintermediate-connector-compatible enclosure. For example, the moduleguides may comprise rails, wherein at least one rail preferably engagesat least one mating guide, such as at least one mating rail, of at leastone module. The module guides preferably extend at least partiallyadjacent to the first surface of the circuit board. The module guidesmay also extend at least partially adjacent to at least one otherstructural component, for example, a substrate structure. The moduleguides are preferably adapted to position interface modules at aseparation distance from the first surface of the circuit board toenhance convective heat transfer. A guide system comprising the moduleguides and mating guides preferably defines perforations to enhanceconvective heat transfer. For example, perforations may be provided inmodule guides, mating guides, and/or both module guides and matingguides to enhance convective heat transfer.

From step 108, the process continues to step 111. In step 111, thecircuit board is installed in an intermediate-connector-compatibleenclosure. The intermediate-connector-compatible enclosure preferablydefines at least one aperture to allow access from the exterior of theintermediate-connector-compatible enclosure to one or more modules thatmay be installed within the intermediate-connector-compatible enclosure.For example, an aperture may be defined so as to provide access from theexterior of the enclosure to a customer connector of a module forconnection of a cable coupled to equipment external to theintermediate-connector-compatible enclosure. Theintermediate-connector-compatible enclosure is preferably fitted withelectromagnetic compliance features, such as shielding, gaskets forapertures, and/or filtering. Following step 111, the initial zero-optionconfiguration has been completed.

From step 111, the process continues at step 112. In step 112, at leastone module is installed in the intermediate-connector-compatibleenclosure. At least one mating intermediate connector of the at leastone module engages at least one of the intermediate connectors of thecircuit board installed in the intermediate-connector-compatibleenclosure. The at least one module preferably comprises at least onemating guide to engage at least one module guide.

In step 113, the product is used, for example, by connecting equipmentexternal to the customer-connector-compatible enclosure to at least onecustomer connector. Optionally, in step 114, at least one module may beuninstalled (i.e., removed) from the intermediate-connector-compatibleenclosure, thereby disconnecting the mating intermediate connector ofthe module from the intermediate connector of the circuit board.Optionally, the process may return to step 112, where at least one othermodule may be installed in the intermediate-connector-compatibleenclosure. Accordingly, modules adapted for use with a circuit board maybe pluggable and removable.

FIG. 2 is a flow diagram illustrating a method in accordance with atleast one embodiment of the present invention for when a circuit boardhas been populated to provide a first set of customer connectors and isto be populated to provide a first set of intermediate connectors. Instep 201, a circuit board is removed from acustomer-connector-compatible enclosure. In step 202, a first set ofcustomer connectors is removed from the circuit board. In step 203, thecircuit board is populated with a first set of intermediate connectors.In step 204, module guides of a guide system are installed on thecircuit board. In step 205, the circuit board is installed in anintermediate-connector-compatible enclosure. Theintermediate-connector-compatible enclosure is compatible with the firstset of intermediate connectors. For example, theintermediate-connector-compatible enclosure may define at least oneaperture to through which a second set of customer connectors may beaccessed from the exterior of the intermediate-connector-compatibleenclosure, wherein the second set of customer connectors is provided byat least one module that is connected to at least a portion of the firstset of intermediate connectors.

FIG. 3 is a flow diagram illustrating a method in accordance with atleast one embodiment of the present invention for when a circuit boardhas been populated to provide the first set of intermediate connectorsand is to be populated to provide the first set of customer connectors.In step 301, a circuit board is removed from anintermediate-connector-compatible enclosure. In step 302, module guidesof a guide system are removed from the circuit board. In step 303, thecircuit board is populated with a first set of customer connectors. Instep 304, the circuit board is installed in acustomer-connector-compatible enclosure. Thecustomer-connector-compatible enclosure is compatible with the first setof customer connectors. For example, the customer-connector-compatibleenclosure may define at least one aperture to through which the firstset of customer connectors may be accessed from the exterior of thecustomer-connector-compatible enclosure.

FIG. 4 is a block diagram illustrating several configurations that maybe provided in accordance with at least one embodiment of the presentinvention. A first example of a configuration is depicted by system 401,which comprises several (e.g., four) modules 402, 403, 404, and 405.Each of modules 402, 403, 404, and 405 provides one customer connector,namely customer connectors 406, 407, 408, and 409, respectively. Asecond example of a configuration is depicted by system 410, whichcomprises several (e.g., three) modules 411, 412, and 413. Modules 411and 412 provide one customer connector each, namely customer connectors414 and 415, and module 413 provides two customer connectors, namelycustomer connectors 416 and 417.

A third example of a configuration is depicted by system 418, whichcomprises several (e.g., two) modules 419 and 420. Module 419 providessingle customer connector 421, and module 420 provides three customerconnectors, namely customer connectors 422, 423, and 424. A fourthexample of a configuration is depicted by system 425, which comprisesseveral (e.g., two) modules 426 and 427. Module 426 provides twocustomer connectors, namely customer connectors 428 and 429, and module427 provides two customer connectors, namely customer connectors 430 and431.

A fifth example of a configuration is depicted by system 432, whichcomprises a module 433. Module 433 provides several (e.g., four)customer connectors, namely customer connectors 434, 435, 436, and 437.As can be seen from the above examples, any combination of any number ofmodules providing any number of customer connectors may be provided.Also, a system may comprise any number of intermediate connectors toconnect to any number of modules.

FIG. 5 is a block diagram illustrating several relationships ofcomponents in accordance with at least one embodiment of the presentinvention. A first example is depicted as a system comprising core 501,intermediate connector (e.g., module connector) 502, customer interface(e.g., ethernet interface) 503, and customer connector (e.g., ethernetconnector) 504. In accordance with such an example, core 501 providessignals suitable for either customer interface 503 or modules that maybe coupled to intermediate connector 502. When a module is connected tointermediate connector 502, customer interface 503 is preferablydisabled (or absent from the system), allowing core 501 to communicatevia the module connected to intermediate connector 501. Unless thesystem is desired to remain in an intermediate-connector-compatibleconfiguration to be ready to accept connection to another module, when amodule is not connected to the system, customer interface 503 ispreferably enabled (or installed and enabled), allowing core 501 tocommunicate via customer interface 503 and customer connector 504.

An example of a situation when such a configuration may be useful iswhen customer interface 503 and customer connector 504 are implementedon the circuit board but utilized circuitry similar to circuitry thatcould otherwise be implemented in a module. In such a situation,customer interface 503 would communicate with core 501 via conductors ofthe circuit board (e.g., PCB traces), bypassing intermediate connector502 (without the need for intermediate connector 502 to be installed onthe circuit board), but communication between core 501 and customerinterface 503 could be implemented using the same signals that wouldotherwise be used for communication between core 501 and a moduleconnected to intermediate connector 502.

A second example is depicted as core 505, intermediate interface (e.g.,module interface) 506, intermediate connector (e.g., module connector)507, standard customer interface (e.g., ethernet interface) 508,standard customer connector (e.g., ethernet connector) 509, standardcustomer interface (e.g., ethernet interface) 510, alternate customerinterface (e.g., other interface) 511, and alternate customer connector(e.g., other connector) 512. In accordance with such an example, core505 is coupled to and provides signals for intermediate interface 506and/or customer interface 508. If present, intermediate interface 506 iscoupled to intermediate connector 507, to which pluggable and removablemodules may be connected. If present, customer interface 508 is coupledto customer connector 509. Access to customer connector 509 may beprovided from the exterior of an enclosure enclosing customer connector509.

However, if a different type of interface and/or connector is desired, aconverter may be provided to convert from the customer connector 509 toan other (e.g., second) customer connector 512. The converter maycomprise customer interface 510, other customer interface 511, and othercustomer connector 512. With such a configuration, customer connector509 is coupled to customer interface 510, which is coupled to othercustomer interface 511, which is coupled to other customer connector512. Other customer interface 511 and other customer connector 512 mayprovide and allow connection to any type of electrical, optical, orother communication interface. Customer connector 509 may be bypassed(and omitted, if desired) if customer interface 508 is coupled tocustomer interface 510 via another route, for example, via conductivepaths of the circuit board. Customer interface 508, customer connector509, and customer interface 510 may be bypassed (and omitted, ifdesired) if core 505 is coupled to other customer interface 511 viaanother route, for example, via conductive paths of the circuit board.

FIG. 6 is a plan view diagram illustrating an example of a system inaccordance with at least one embodiment of the present invention. Thesystem comprises intermediate-connector-compatible enclosure 601; powersupply 602; circuit board 603; first surface components 604;intermediate connectors 605, 606, 607, and 608; customer connectorsolder pads 609, 610, 611, 612; module guides 613, 614, 615, 616, and617; and substrate structure 618. Enclosure 601 defines apertures 619,620, 621, and 622 to allow access from the exterior ofintermediate-connector-compatible enclosure 601 to modules that may beinstalled in intermediate-connector-compatible enclosure 601.Alternatively, one or more apertures may be defined over the area overwhich apertures 619, 620, 621, and 622 are defined. Blank plates may beprovided to fill in any of the apertures, for example, to provide aphysical and electromagnetic barrier when respective modules are notinstalled in intermediate-connector-compatible enclosure 601. Theapertures may be defined proximate to a first (e.g., front) enclosureend of intermediate-connector-compatible enclosure 601.

Substrate structure 618 is preferably located proximate to the first endof intermediate-connector-compatible enclosure 601. Substrate structure618 provides a first substrate surface that is preferably coplanar witha first surface of circuit board 603. A first (e.g., front) circuitboard end of circuit board 603 is preferably located in proximity to asecond substrate end of substrate structure 618 opposite a firstsubstrate end of substrate structure 618, wherein the first substrateend is preferably located in proximity to the first enclosure end ofintermediate-connector-compatible enclosure 601. A second (e.g., rear)circuit board end of circuit board 603 opposite the first circuit boardend is preferably located in proximity to a first (e.g., front) powersupply end of power supply 602. A second (e.g., rear) power supply endof power supply 602 is preferably located opposite the first powersupply end and in proximity to a second (e.g., rear) enclosure end ofintermediate-connector-compatible enclosure 601, wherein the secondenclosure end is preferably located opposite the first enclosure end. Bylocating power supply 602 beyond the perimeter of circuit board 603, thedimensions of power supply 602 are not constrained by the dimensions ofcircuit board 603, allowing circuit board 603 to extend over any portionof a space defined between a third (e.g., top) end and a fourth (e.g.,bottom) end of intermediate-connector-compatible enclosure 601, as wellas over any portion of a space defined between a fifth (e.g., left) anda sixth (e.g., right) end of intermediate-connector-compatible enclosure601.

Customer connector solder pads 609, 610, 611, and 612 are preferablylocated proximate to the first circuit board end and distal to thesecond circuit board end. Intermediate connectors 605, 606, 607, and 608are preferably located on a side of customer connector solder pads 609,610, 611, and 612 opposite the first circuit board end and toward thesecond circuit board end. Intermediate connectors 605, 606, 607, and 608are preferably located closer to the second circuit board end than thefirst circuit board end to maximize space for modules that may becoupled to intermediate connectors 605, 606, 607, and 608, but firstsurface components 604 may be mounted on circuit board 603 betweenintermediate connectors 605, 606, 607, and 608 and the second circuitboard end. First surface components 604 are preferably mounted oncircuit board 603 proximate to the second circuit board end and distalto the first circuit board end. By mounting first surface components 604on a first (e.g., top) surface of circuit board 603, first surfacecomponents 604 may be approximately as tall as any modules that may beconnected to intermediate connectors 605, 606, 607, and 608, as thedistance between the first surface of circuit board 603 and a third(e.g., top) end of intermediate-connector-compatible enclosure 601 maybe approximately similar for areas of the first surface of circuit board603 over which intermediate connectors 605, 606, 607, and 608 and firstsurface components 604 may be mounted. Accordingly, depending on thedistance between the second (e.g., bottom) surface of circuit board 603and a fourth (e.g., bottom) end of intermediate-connector-compatibleenclosure 601, the height of components (e.g., first surface components604) that may be mounted on the first surface of circuit board 603 maybe greater than the height of components that may be mounted on thesecond surface of circuit board 603. However, components may be mountedon the second surface of circuit board 603, even over an area betweenthe first circuit board end and intermediate connectors 605, 606, 607,and 608, while the area between the first circuit board end andintermediate connectors 605, 606, 607, and 608 is preferably kept clearof any components having a height sufficient to interfere with anymodules that may be installed in proximity to such an area. By notinstalling customer connectors on customer connector solder pads 609,610, 611, and 612, interference with any modules that may be installedmay be further avoided or minimized.

Module guides 613, 614, 615, 616, and 617 are preferably installed so asto extend from a first substrate surface of substrate structure 618proximate to the first substrate end of the substrate structure 618 tothe first surface of circuit board 603 proximate to intermediateconnectors 605, 606, 607, and 608. Module guides 613, 614, 615, 616, and617 help define paths through which modules may be inserted to connectto intermediate connectors 605, 606, 607, and 608. For example, moduleguides 613 and 614 help define a path from aperture 619, over substratestructure 618, over customer connector solder pads 609 and a portion ofthe first surface of circuit board 603, to intermediate connector 605.As another example, module guides 614 and 615 help define a path fromaperture 620, over substrate structure 618, over customer connectorsolder pads 610 and a portion of the first surface of circuit board 603,to intermediate connector 606. As yet another example, module guides 615and 616 help define a path from aperture 621, over substrate structure618, over customer connector solder pads 611 and a portion of the firstsurface of circuit board 603, to intermediate connector 607. As one moreexample, module guides 616 and 617 help define a path from aperture 622,over substrate structure 618, over customer connector solder pads 612and a portion of the first surface of circuit board 603, to intermediateconnector 608. The paths defined by module guides 613, 614, 615, 616,and 617 have axes parallel to the module guides defining those paths.

FIG. 7 is a prospective view diagram illustrating an example of a systemin accordance with at least one embodiment of the present invention.Module guides 613 and 614 are attached to substrate structure 618 and/orcircuit board 603. Module guides 613 and 614 preferably provide linearrails that are parallel to one another and that are adapted to engage,preferably slidably, mating guides 626 and 643. Mating guides 626 and643 are attached to module circuit board 630. Mating guides 626 and 643preferably provide linear rails that are parallel to one another andthat adapted to engage, preferably slidably, module guides 613 and 614.Module first surface components 631, 632, 633, and 634 are mounted on amodule first surface of module circuit board 630. Accordingly, thesystem accommodates installation and removal of a module comprisingmodule circuit board 630, mating guides 626 and 643, and module firstsurface components 631, 632, 633, and 634.

FIG. 8 is an elevation view diagram illustrating an example of a systemin accordance with at least one embodiment of the present invention. Thesystem comprises intermediate-connector-compatible enclosure 601, powersupply 602, circuit board 603, first (e.g., top) surface component 604,intermediate connector 605, second (e.g., bottom) surface components623, 624, and 625, customer connector solder pads 609, module guide 613,mating guide 626, substrate structure 618, module circuit board 630,module first (e.g., top) surface components 631, 632, 633, and 634,module second (e.g., bottom) surface components 635, 636, 637, and 638,module interconnect 639, mating intermediate connector 640, andstandoffs 641 and 642. The guide system comprising module guide 613 andmating guide 626 defines perforations 627, 628, and 629 to enhanceconvective heat transfer. Standoffs 641 and 642 position circuit board603 a standoff distance away from the interior of the second end ofintermediate-connector-compatible enclosure 601 to allow space toaccommodate the height of second surface components 623, 624, and 625and to promote convective heat transfer.

As illustrated, since power supply 602 is preferably located between thesecond end of circuit board 603 and the second end ofintermediate-connector-compatible enclosure 601, power supply 602 mayoccupy the entire space between those ends from interior of the thirdend of intermediate-connector-compatible enclosure 601 to the interiorof the four end of intermediate-connector-compatible enclosure 601 orany portion thereof. First surface component 604 is preferably mountedon a first surface of circuit board 603 and may occupy a space betweenintermediate connector 605 and the second end of circuit board 603having a height no greater than a distance from the first surface ofcircuit board 603 to the interior of the third end ofintermediate-connector-compatible enclosure 601 or any portion thereof.

Second surface components 623, 624, and 625 are preferably mounted onthe second surface of circuit board 603 and may occupy a space over thesecond surface of circuit board 603 (excluding any space occupied bystandoffs 641 and 642) between the second surface of circuit board 603and the interior of the fourth end of intermediate-connector-compatibleenclosure 601. Locating second surface components 623, 624, and 625 onthe second surface of circuit board 603 can help reduce the need forcomponents to be mounted on the first surface of circuit board 603,maximizing a flat (and preferably bare) area of the first surface ofcircuit board 603 over which module guide 613 and mating guide 626 maybe positioned. Mating guide 626 engages, preferably slidably, moduleguide 613. Mating guide 626 is coupled to module circuit board 630.Module first surface components 631, 632, 633, and 634 are mounted on amodule first (e.g., top) surface of module circuit board 630. Modulesecond surface components 635, 636, 637, and 638 are mounted on a modulesecond (e.g., bottom) surface of module circuit board 630.

Module guide 613 and mating guide 626 position module circuit board 630at a separation distance from substrate structure 618 and circuit board603 so as to enhance convective heat transfer. Either module guide 613or mating guide 626 may define perforations 627, 628, and 629, or bothmodule guide 613 and mating guide 626 may define perforations to enhanceconvective heat transfer. Given the separation distance provided by theguide system, module second surface components 635, 636, 637, and 638may occupy a space over the module second surface of module circuitboard 630 between the module second surface of module circuit board 630and the first surface of circuit board 603 and/or the surface ofsubstrate structure 618, as the first surface of circuit board 603 andthe surface of substrate structure 618 preferably lie in the same plane.Substrate structure 618 may be attached so as to maintain a coplanarrelationship with circuit board 603, for example by attaching substratestructure 618 to standoffs 641 and 642, either directly or through anintermediate mechanical structure, such as intermediate-connectorcompatible enclosure, which may be coupled to substrate structure 618and circuit board 603. Module first surface components 631, 632, 633,and 634 may occupy a space over the module first surface of modulecircuit board 630 between the module first surface of module circuitboard 630 and the interior of the first end ofintermediate-connector-compatible enclosure 601.

To accommodate the separation distance provided by the guide system, amodule interconnect 639 coupled to a mating intermediate connector 640,which mates with intermediate connector 605, may be provided to coupleconductors of module circuit board 630 to mating intermediate connector640 and to span the distance from module circuit board 630 tointermediate connector 605. Module interconnect 639 is preferablycoupled to the module second surface of module circuit board 630.

FIG. 9 is a cross-sectional diagram illustrating an example of a moduleguide subsystem in accordance with at least one embodiment of thepresent invention. Module guides 613 and 614 are mounted on substratestructure 618 (and/or circuit board 603), preferably along axes parallelto one another. Mating guides 626 and 643 are mounted on module circuitboard 630, preferably along axes parallel to one another, and preferablyon the module second surface of the module circuit board 630. Matingguide 626 engages, preferably slidably, module guide 613. Mating guide643 engages, preferably slidably, module guide 614. Module first surfacecomponents, such as module first surface component 631, may be mountedon the module first surface of module circuit board 630. Module secondsurface components, such as module second surface component 635, may bemounted on the module second surface of the module circuit board 630.The guide system comprising module guides 613 and 614 and mating guides626 and 643 maintain module circuit board 630 at a separation distancefrom substrate structure 618, wherein the separation distance preferablyprovides a sufficient air duct to enhance convective heat transfer toremove heat from components of the system that dissipate heat.

FIG. 10 is an elevation view diagram illustrating an example of a moduleguide subsystem in accordance with at least one embodiment of thepresent invention. Module guide 614 is mounted on substrate structureand/or circuit board 603, which are preferably coplanar. For example,module guide 614 may provide a linear rail to slidably engage matingguide 626. A module comprises module circuit board 630, mating guide626, and module first surface component 631. Mating guide 626 is mountedon module circuit board 630. Module first surface component 631 ismounted on the first surface of module circuit board 630. Preferably,mating guide 626 and/or module guide 614 define perforations 627, 628,629, and 644, which allow ventilation across the guide system, therebyenhancing convective heat transfer. As illustrated, perforations 627,628, 629, and 644 may be implemented as elongated perforations, such aselongated rectangular perforations. Alternatively, perforations 627,628, 629, and 644 may be implemented as a series of non-elongatedperforations, for example, round or square perforations.

FIG. 11 is a plan view diagram illustrating an example of a module guidesubsystem in accordance with at least one embodiment of the presentinvention. From such a view, module circuit board 630 and module firstsurface component 631 are visible, and features of the guide subsystemare denoted by dashed lines. The module comprises module circuit board630 and module first surface component 631 mounted on the module firstsurface of the module circuit board 630.

FIG. 12 is a prospective view diagram illustrating an example of asystem incorporating a stackable module guide subsystem in accordancewith at least one embodiment of the present invention. Module guides 613and 614 are attached to a first surface of circuit board 603 (andoptionally may be continued over a substrate structure 618). Matingguides 626 and 643 are attached to a first module second surface of afirst module, preferably first module circuit board 630. Mating guides626 and 643 are adapted to engage module guides 613 and 614,respectively.

Module guides 646 and 647 are attached to a first module first surfaceof the first module, preferably first module circuit board 630. Matingguides 648 and 649 are attached to a second module second surface of asecond module, preferably second module circuit board 650. Mating guides648 and 649 are adapted to engage module guides 646 and 647,respectively. Second module first surface components 651, 652, 653, and654 are mounted on a second module first surface of second modulecircuit board 650.

Several intermediate connectors at several distances from circuit board603 may be provided to engage and couple signals to and from the firstand second modules and/or an additional intermediate connector may beprovided on the first module to couple the second module (e.g., in adaisy-chained manner). Perforations to enhance convective heat transferare preferably provided for both the first guide subsystem comprisingmodule guides 613 and 614 and mating guides 626 and 643 and the secondguide subsystem comprising module guides 646 and 647 and mating guides648 and 649.

FIG. 13 is an elevation view diagram illustrating an example of a systemincorporating a stackable module guide subsystem in accordance with atleast one embodiment of the present invention. Several modules may beinstalled at one or more levels with respect to circuit board 603.Module guides of circuit board 603 are adapted to couple with matingguides of one or more modules at a first level, such as modulesillustrated with reference to module circuit boards 630, 655, and 656.One or more modules at a second level with respect to circuit board 603,such as modules illustrated with reference to module circuit boards 657,658, and 659, may be installed such that their mating guides engage oneor more module guides of one or more modules installed at the firstlevel. One or more modules at a third level with respect to circuitboard 603, such as the module illustrated with reference to modulecircuit board 660, may be installed such that their mating guides engageone or more module guides of one or more modules installed at the secondlevel.

As can be seen from the illustrated example, various combinations ofmodules of various sizes may be installed. For example, the illustratedexample depicts two one-port modules and one two-port module installedat the first level, a two-port module and two one-port modules installedat the second level, and one four-port module installed at the thirdlevel. As illustrated, various numbers of modules of various numbers ofports may be installed at one or more of several levels without the typeof modules on any one level imposing constraints as to the type ofmodules and their configuration on any other level. However, for anygiven level, a sufficient number of modules should preferably beinstalled at the preceding level to provide sufficient mechanicalstability.

As shown in the illustrated example, module guides and mating guides ofa guide subsystem in accordance with at least one embodiment of thepresent invention may have cross sections in a variety of designs, forexample, those that approximate the shapes of the letters C or U, I orH, T, L or J, F, E, V, M, K, N or Z, etc., wherein at least a portion ofa module guide engages at least a portion of a mating guide to define amechanical relationship between a circuit board and a module or betweena module of one level and a module of a succeeding level.

As shown in FIG. 13, a system in accordance with at least one embodimentmay comprise a chassis and a first module. The chassis may comprise afirst module guide. The first module may comprise a first mating guide.The first mating guide may be adapted to slidably engage the firstmodule guide. However, the first mating guide may be unable to engage asecond module. The inability to engage the second module may be providedby limiting the first mating guide to providing a mechanical interfacebetween the first module and the chassis and not configuring it toprovide a mechanical interface between a second module and the chassis.

When the chassis comprises a second module guide not engaged by thefirst mating guide but spanned by the first module, the first module andthe second module guide preferably define a clearance to allow movementof the first module relative to the second module guide withoutinterference. By spanning the second module guide, the first moduleextends to and engages module guides on both sides of the second moduleguide, but does not engage the second module guide. The first moduleneed not engage module guides immediately adjacent to the second moduleguide, but may span multiple module guides. Spanned module guides mayalso be referred to as unused module guides.

In accordance with at least one embodiment, the first mating guide ismounted on a first surface (e.g., a surface closer to the first moduleguide) of the first module. The first module preferably furthercomprises a second module guide mounted on a second surface (e.g., asurface farther from the first module guide) of the first module. Thesecond surface is preferably opposite the first surface. The secondmodule guide is preferably adapted to engage a second mating guide of asecond module.

In accordance with at least one embodiment, the first mating guide ismounted on a first surface of the first module parallel to a first edgeof the first surface so as to define an unpopulated area of the firstsurface between the first mating guide and the first edge. Theunpopulated area is an area where the first surface extends but is notcovered by the first mating guide or other objects, for example,electronic components. The unpopulated area exposes the first edge ofthe first surface (e.g., a card edge of a circuit board of the firstmodule) allowing engagement of the first edge with a card edge moduleguide without interference with the first mating guide. Suchinterference would result if the first mating guide were positioned soas to block engagement of the first edge with the card edge moduleguide.

In accordance with at least one embodiment, the first module comprises afirst circuit board, wherein first mating guide engages the first moduleguide at an angle that is not perpendicular to a plane of the firstcircuit board and at a location that is offset from the plane of thefirst circuit board. Although the actual engagement of the first matingguide with the first module guide may involve several segments atseveral angles, the angle referred to above should be understood to bean axis of a significant terminal portion of the first mating guideand/or the first module guide. A location that is offset from the planeshould be understood to be a location that lies outside of the plane ofthe first circuit board. In accordance with at least one embodiment, thefirst module guide has a T-shaped cross section.

In accordance with at least one embodiment, a chassis comprises a firstmodule guide. The first module guide is preferably adapted to slidablyengage a first mating guide of a first module. The first mating guidepreferably does not extend through a plane of a circuit board of thefirst module outside a perimeter of the circuit board.

Preferably, the chassis comprises a second module guide adapted to bespanned by the first module, wherein the second module guide defines aclearance to allow movement of the first module relative to the secondmodule guide without the first module contacting the second moduleguide. The clearance may be defined between the second module guide andthe portion of the first module that extends closest to the secondmodule guide, for example, an electronic component mounted on a surfaceof a circuit board of the first module.

Preferably, the chassis comprises a plurality of module guidescomprising the first module guide, wherein the plurality of moduleguides are adaptable to slidably engage a plurality of modules.Preferably, a first portion of the plurality of modules has a firstmodule width and a second portion of the plurality of modules has asecond module width, the first module width being different than thesecond module width. For example, the first module width may be a singleunit width wherein the first module engages adjacently disposed moduleguides, while the second module width may be a two unit width whereinthe second module spans an unused module guide and engages module guidesadjacent to and on both sides of the unused module guide. Preferably,the first module of the first module width may be removed and replacedby a second module of the second module width without removal of any ofthe module guides.

Preferably, the chassis is adapted to engage a card edge module guide,the card edge module guide extending into the plane of the circuit boardand beyond both sides of the plane of the circuit board and adapted toengage a first edge of the circuit board. Preferably, the first moduleguide is adapted to engage the first mating guide at an angle that isnot perpendicular to a plane of the first circuit board and at alocation that is offset from the plane of the first circuit board.Preferably, the first module guide has a T-shaped cross section.

In accordance with at least one embodiment, a first module comprises afirst mating guide adapted to slidably engage a first module guide of achassis but is unable to engage a second module. Preferably, the firstmating guide does not extend through a plane of a circuit board of thefirst module outside a perimeter of the circuit board. Preferably, thefirst module is adapted to span a second module guide of a chassis,wherein the second module guide not engaged by the first mating guideand the first module defines a clearance to allow movement of the firstmodule relative to the second module guide without the first modulecontacting the second module guide.

Preferably, the first mating guide is mounted on a first surface of thefirst module. Preferably, the first module further comprises a secondmodule guide mounted on a second surface of the first module, whereinthe second surface is opposite the first surface. Preferably, the secondmodule guide is adapted to engage a second mating guide of a secondmodule.

Preferably, the first mating guide is mounted on a first surface of thefirst module parallel to a first edge of the first surface so as todefine an unpopulated area of the first surface between the first matingguide and the first edge, allowing engagement of the first edge with acard edge module guide without interference with the first mating guide.Preferably, the first module comprises a first circuit board, whereinfirst mating guide is adapted to engage the first module guide at anangle that is not perpendicular to a plane of the first circuit boardand at a location that is offset from the plane of the first circuitboard.

In accordance with at least one embodiment, a first module guide isadapted to be mountable on a first chassis surface of a chassisstructure and adaptable to engage a first mating guide mounted on afirst module surface of a module. Preferably, the first module guidedefines a gap between the first module guide and the first modulesurface.

Preferably, the first module guide has a first module guide crosssection comprising a first module guide cross section portion extendingin first direction away from the first chassis surface and a secondmodule guide cross section portion coupled to the first cross sectionportion distal to the first chassis surface, the second module guidecross section portion extending in a second direction at a first moduleguide angle to the first direction. Preferably, the first module guidecross section is a T-shaped cross section. Preferably, the first matingguide has a first mating guide cross section comprising a first matingguide cross section portion extending in a third direction opposite thefirst direction and a second mating guide cross section portion coupledto the first mating guide cross section portion distal to the firstmodule surface, the second mating guide cross section portion extendingin a fourth direction at a mating guide angle to the third direction.Preferably, the fourth direction opposes the second direction.

Thus, a method and apparatus for a fixed and replaceable modulearchitecture data path interface has been presented. Although theinvention has been described using certain specific examples, it will beapparent to those skilled in the art that the invention is not limitedto these few examples. For example, although the invention has beendescribed with respect to particular examples of connectors, moduleguides, etc., the invention may be used in systems with other types ofsuch features that may have other characteristics, for example, othertypes of connector and/or other designs of module guides. Otherembodiments utilizing the inventive features of the invention will beapparent to those skilled in the art, and are encompassed herein.

1. Apparatus comprising: a chassis comprising a first module guide; anda first module comprising a first mating guide, the first mating guideadapted to slidably engage the first module guide but unable to engage asecond module.
 2. The apparatus of claim 1 wherein, when the chassiscomprises a second module guide not engaged by the first mating guidebut spanned by the first module, the first module and the second moduleguide define a clearance to allow movement of the first module relativeto the second module guide without interference.
 3. The apparatus of theclaim 1 wherein the first mating guide is mounted on a first surface ofthe first module and wherein the first module further comprises a secondmodule guide mounted on a second surface of the first module, whereinthe second surface is opposite the first surface, the second moduleguide adapted to engage a second mating guide of a second module.
 4. Theapparatus of claim 1 wherein the first mating guide is mounted on afirst surface of the first module parallel to a first edge of the firstsurface so as to define an unpopulated area of the first surface betweenthe first mating guide and the first edge, allowing engagement of thefirst edge with a card edge module guide without interference with thefirst mating guide.
 5. The apparatus of claim 1 wherein the first modulecomprises a first circuit board, wherein first mating guide engages thefirst module guide at an angle that is not perpendicular to a plane ofthe first circuit board and at a location that is offset from the planeof the first circuit board.
 6. The apparatus of claim 1 wherein thefirst module guide has a T-shaped cross section.
 7. Apparatuscomprising: a chassis comprising a first module guide, the first moduleguide adapted to slidably engage a first mating guide of a first module,the first mating guide not extending through a plane of a circuit boardof the first module outside a perimeter of the circuit board.
 8. Theapparatus of claim 7 wherein the chassis comprises a second module guideadapted to be spanned by the first module, wherein the second moduleguide defines a clearance to allow movement of the first module relativeto the second module guide without the first module contacting thesecond module guide.
 9. The apparatus of claim 7 wherein the chassiscomprises a plurality of module guides comprising the first moduleguide, wherein the plurality of module guides are adaptable to slidablyengage a plurality of modules, wherein a first portion of the pluralityof modules has a first module width and a second portion of theplurality of modules has a second module width, the first module widthbeing different than the second module width.
 10. The apparatus of claim9 wherein the first module of the first module width may be removed andreplaced by a second module of the second module width without removalof any of the module guides.
 11. The apparatus of claim 7 wherein thechassis is adapted to engage a card edge module guide, the card edgemodule guide extending into the plane of the circuit board and beyondboth sides of the plane of the circuit board and adapted to engage afirst edge of the circuit board.
 12. The apparatus of claim 7 whereinthe first module guide is adapted to engage the first mating guide at anangle that is not perpendicular to a plane of the first circuit boardand at a location that is offset from the plane of the first circuitboard.
 13. The apparatus of claim 7 wherein the first module guide has aT-shaped cross section.
 14. Apparatus comprising: a first modulecomprising a first mating guide adapted to slidably engage a firstmodule guide of a chassis but unable to engage a second module.
 15. Theapparatus of claim 14 wherein the first mating guide does not extendthrough a plane of a circuit board of the first module outside aperimeter of the circuit board.
 16. The apparatus of claim 14 whereinthe first module is adapted to span a second module guide of a chassis,wherein the second module guide not engaged by the first mating guideand the first module defines a clearance to allow movement of the firstmodule relative to the second module guide without the first modulecontacting the second module guide.
 17. The apparatus of the claim 14wherein the first mating guide is mounted on a first surface of thefirst module and wherein the first module further comprises a secondmodule guide mounted on a second surface of the first module, whereinthe second surface is opposite the first surface, the second moduleguide adapted to engage a second mating guide of a second module. 18.The apparatus of claim 14 wherein the first mating guide is mounted on afirst surface of the first module parallel to a first edge of the firstsurface so as to define an unpopulated area of the first surface betweenthe first mating guide and the first edge, allowing engagement of thefirst edge with a card edge module guide without interference with thefirst mating guide.
 19. The apparatus of claim 14 wherein the firstmodule comprises a first circuit board, wherein first mating guide isadapted to engage the first module guide at an angle that is notperpendicular to a plane of the first circuit board and at a locationthat is offset from the plane of the first circuit board.
 20. Apparatuscomprising: a first module guide adapted to be mountable on a firstchassis surface of a chassis structure and adaptable to engage a firstmating guide mounted on a first module surface of a module, wherein thefirst module guide defines a gap between the first module guide and thefirst module surface.
 21. The apparatus of claim 20 wherein the firstmodule guide has a first module guide cross section comprising: a firstmodule guide cross section portion extending in first direction awayfrom the first chassis surface; and a second module guide cross sectionportion coupled to the first cross section portion distal to the firstchassis surface, the second module guide cross section portion extendingin a second direction at a first module guide angle to the firstdirection.
 22. The apparatus of claim 21 wherein the first module guidecross section is a T-shaped cross section.
 23. The apparatus of claim 21wherein the first mating guide has a first mating guide cross sectioncomprising: a first mating guide cross section portion extending in athird direction opposite the first direction; and a second mating guidecross section portion coupled to the first mating guide cross sectionportion distal to the first module surface, the second mating guidecross section portion extending in a fourth direction at a mating guideangle to the third direction.
 24. The apparatus of claim 23 wherein thefourth direction opposes the second direction.